Apparatus for preventing sparks in the ignition system of an engine while the engine is at rest

Abstract

The voltage in the secondary of an ignition coil is prevented from reaching an amplitude at which a spark might be created by a Zener diode connected in parallel with the series transistor acting as a switch which interrupts the current through the primary winding of the coil. Upon breakdown of the Zener diode, the series transistor is switched to the conductive state briefly, thereby preventing further voltage build-up in the secondary. When the engine is in operation, a transistor which forms part of a voltage divider is switched to the conductive state, connecting the voltage divider between the secondary winding and the Zener diode. The voltage divider is so dimensioned that the Zener diode will respond to a voltage slightly less than the breakdown voltage of the emitter-collector circuit of the series transistor, but higher than the voltage required for creating a spark.

I claim: 
     
       1. In an ignition system for internal combustion engine having a source of DC voltage an ignition coil (8) connected to said source of DC voltage, said ignition coil having a primary winding and a secondary winding, spark producing means connected to said secondary winding, output switch means (7) connected in series with said primary winding and having a conductive and a nonconductive state respectively permitting and blocking current flow through said primary winding, whereby switching said output switch means from said conductive to said nonconductive state induces a secondary voltage across said secondary winding and a spark in said spark producing means if said secondary voltage exceeds a predetermined secondary voltage, said ignition system further having first control means (3-6, 13) for switching said output switch means from said conductive to said nonconductive state if said output switch means is in said conductive state when said engine is at rest:   apparatus for preventing the furnishing of a spark while the engine is at rest, comprising, in accordance with the invention, second control means (22, 16) connected to said output switch means and responsive to said secondary voltage, for switching said output switch means briefly back to said conductive state when said secondary voltage reaches a limiting secondary voltage less than said predetermined secondary voltage, whereby current flow through said primary winding limits the voltage build-up in said secondary winding.   
     
     
       2. A system as set forth in claim 1, further comprising third control means (19, 20, 21) connected between said ignition coil and said second control means, and operative only in response to a first control signal, for decreasing the voltage applied to said second control means, whereby said second control means switches said output switch means to said conductive state only when said secondary voltage exceeds said predetermined secondary voltage; and wherein said first control means comprises means for furnishing said first control signal only when said engine is in operation, whereby sparks can be created by said spark creating means during operation of said engine.   
     
     
       3. A system as set forth in claim 2, wherein said output switch means comprises an output transistor. 
     
     
       4. A system as set forth in claim 3, wherein said second control means comprises a Zener diode (22). 
     
     
       5. A system as set forth in claim 4, wherein said output transistor has an emitter-collector circuit connected in series with said primary winding of said ignition coil; wherein said emitter-collector circuit has a maximum permissable breakdown voltage when said output transistor is in said nonconductive state;   and wherein said second control means switches said output transistor briefly to said conductive state when said decreased voltage is a predetermined decreased voltage corresponding to a voltage less than said predetermined breakdown voltage of said emitter-collector circuit of said output transistor.